The catalytic oxydehydrogenation of olefins for the production of butadiene and isoprene has been the subject of continued interest for many years. The prior art encompasses catalysts consisting of elements which appear to cover the entire spectrum of the Periodic Table. Particular oxydehydrogenation catalysts are disclosed in U.S. Pat. Nos. 2,991,321; 2,991,322; 3,067,272; 3,110,746; 3,119,111. An all-important requirement in the commercial production of any chemical by catalytic oxidation is that the catalyst exhibit not only high conversion but extremely high selectivity for long periods of time. The foregoing patents, drawn to oxydehydrogenation catalysts, are disclosed to be generally effective in several reactions. The instant catalyst on the other hand, is particularly and unexpectedly effective in the conversion of isoamylenes, methyl butanols, or diisoamylene to isoprene, despite the presence of an alkali metal as an essential ingredient, and a relatively high content of Group VIII Fourth Period element.
This invention relates to oxydehydrogenation catalysts consisting essentially of an alkali metal as an essential catalytic ingredient in combination with oxides of bismuth, molybdenum and iron. The instant alkali metal containing catalyst is an improvement over prior art catalysts in that it is particularly suited to the catalytic oxydehydrogenation of isoamylenes, methyl butanols or mixtures thereof to isoprene.
It is noteworthy that, in general, a catalyst particularly effective in one oxydehydrogenation reaction is conspicuously unable to perform as well in another. For example, an oxydehydrogenation catalyst containing the oxides of bismuth, molybdenum, iron and nickel is disclosed in U.S. Pat. No. 3,414,631, and it is particularly efficient in the oxydehydrogenation of butene to butadiene but significantly less effective in the conversion of isoamylenes to isoprene. This peculiar and unexplained preference of a catalyst for one reaction over another apparently analogous one, is reflected and focused by the absence of examples disclosing analyses of the products of reaction in a number of prior art disclosures. In any event, there is significant utility of the instant invention in the catalytic oxidation of olefins to unsaturated aldehydes and acids, and for the catalytic ammoxidation of olefins to unsaturated nitriles.